Various apparatuses such as controllers, information apparatus, and audio apparatus are loaded on vehicles. This results in a need for co-operations and information sharing between on-vehicle apparatuses.
For this reason, a network for information communication is constructed by connecting an on-vehicle apparatus which must co-operate and share information among various apparatuses loaded on a vehicle with a dedicated communication line such that information can be transmitted and received between the apparatuses (on-vehicle LAN).
However, the number of networks constructed on a vehicle recently increases as a result of increases in the number and types of on-vehicle apparatuses or improvements of functions of on-vehicle apparatuses. There is also a trend toward smaller vehicle sizes as a result of increases in the price of fuel. This has made it difficult to incorporate on-vehicle apparatuses in a vehicle by providing a communication line for each of networks in the vehicle.
In order to solve this inconvenience, it is proposed to use a power supply cable provided to supply power to each on-vehicle apparatus from a battery as a communication line. This is referred to as power supply cable communication.
However, the number of apparatuses that can be loaded on a vehicle will be limited unless the size of on-vehicle apparatuses is reduced. When the electrical apparatuses as on-vehicle apparatuses increases, noise in a vehicle becomes more severe, which increases instances in which errors can occur in communication in a network.
For example, when a pattern connecting a data communication section and a power supply section is formed on a printed circuit board (substrate) in an on-vehicle apparatus to supply power from the power supply section to the data communication section, noise enters through the pattern and adversely affects the on-vehicle apparatus. The noise is also released from the pattern to adversely affect the on-vehicle apparatus.